Generally described, steam turbines and the like may have a defined steam path that includes a steam inlet, a turbine section, and a steam outlet. Steam leakage, either out of the steam path, or into the steam path from an area of higher pressure to an area of lower pressure, may adversely affect the operating efficiency of the steam turbine. For example, steam path leakage in the steam turbine between a rotating shaft and a circumferentially surrounding turbine casing may lower the overall efficiency of the steam turbine.
Steam generally may flow through a number of turbine stages typically disposed in series through first-stage blades such as guides and runners (or nozzles and buckets) and subsequently through guides and runners of later stages of the turbine. In this manner, the guides may direct the steam toward the respective runners, causing the runners to rotate and drive a load, such as an electrical generator and the like. The steam may be contained by circumferential shrouds surrounding the runners, which also may aid in directing the steam or combustion gases along the path. In this manner, the turbine guides, runners, and shrouds may be subjected to high temperatures resulting from the steam, which may result in the formation of hot spots and high thermal stresses in these components. Because the efficiency of a steam turbine is dependent on its operating temperatures, there is an ongoing demand for components positioned along the steam or hot gas path to be capable of withstanding increasingly higher temperatures without failure or decrease in useful life.
Certain turbine blades may be formed with an airfoil geometry. The blades may be attached to tips and roots, where the roots are used to couple a blade to a disc or drum. The turbine blade geometry and dimensions may result in certain profile losses, secondary losses, leakage losses, mixing losses, and the like that may adversely affect efficiency and/or performance of a steam turbine.
In some cases, e.g., steam delivery on the saturation line from a Pressurized Water Reactor, the turbine may operate with wet steam flows. Such flows may create additional wetness losses via the non-equilibrium expansion of the steam (which generates fine fog) and consequential coarse water losses.